The present invention relates to a writing pen. More particularly, the invention relates to a writing pen of the type in which a flow-regulator having an outer circumference formed with a labyrinth groove is interposed between the writing tip and an ink reservoir in a pen barrel and in which an ink supply rod is fitted in an internal through-bore of the flow-regulator. Yet more specifically, the invention relates to a writing pen having an improved flow-regulator which is suitable for supplying ink to a fine writing tip and in which first, second and third ink supply rods are connected in series in the internal through-bore of the flow-regulator.
There has been proposed in the art a writing pen of the type in which an ink supply rod is fitted in an internal through-hole of a flow-regulator having its circumference formed with a labyrinth groove thereby to control the flow of ink to the writing tip. Examples of such pens are disclosed in U.S. Pat. Nos. 4,239,408 and 4,382,707. However, the pens of these proposals do not satisfactorily solve the requirements of ink flow control to a tip suitable for fine writing over wide ranges of atmospheric pressure and ambient temperature. This will be described below more in detail.
In a writing pen having an ink supply rod inserted into a flow-regulator, the distance from the ink reservoir to the writing tip is greater than in a pen having no flow-regulator due to the axial length occupied by the flow-regulator. In a pen as disclosed in the above-mentioned U.S. Pat. No. 4,382,707, which pen employs a single ink supply rod, the ink supply rod is unable to supply ample ink to the writing tip if the supply rod is desirably thin. Alternatively, in the case of a tubular body formed with an ink passage extending straightly in the axial direction, if an impact force is imposed on the pen or the pen is held upright for a significant period of time, the ink is liable to be forced back toward the reservoir away from the tip, making it impossible to write with the pen. Therefore, the ink supply rod in a pen of this kind has to have a relatively large diameter and be made of a porous material. Unavoidably, the external diameter of the flow-regulator is accordingly made larger, making it difficult to design a pen having a thin body, resulting in a pen construction suitable only for a writing pen having a wide point and a relatively thick body.
On the other hand, a pen using a combination of two different ink supply rods, as disclosed in U.S. Pat. No. 4,239,408, is more suitable for use with a fine writing tip than the pen using a single ink supply rod, but this pen is disadvantageous in that it suffers from a danger of ink leakage.